1. Field of the Invention
The invention relates to an over-driving device, and more particularly to an over-driving device applied in a display panel.
2. Description of the Related Art
FIGS. 1A and 1B respectively show the variations of gray values and brightness of a pixel when a response time of a liquid crystal display panel is excessively long. Referring FIGS. 1A and 1B, in an ideal situation, when the desired gray value of a pixel is changed from G0 to G1 at time point T0, the brightness thereof is changed from L0 to L1. However, since the rotational speed of liquid crystal molecules of a pixel is slow, the response time during which the brightness is changed from L0 to L1 is excessively long, and the brightness reaches L1 at time point T2. Thus, the brightness of the pixel can not reach the desired degree L1 in a frame.
Since large-sized liquid crystal display panels are continuously being developed, it is important to shorten response time of a liquid crystal display panel. In order to solve the problem of a long response time, an over-driving method is used. FIGS. 2A and 2B respectively show the variations of gray values and brightness of a pixel utilizing an over-driving method. Referring to FIG. 2A, to shorten response time, the desired gray value of a pixel is changed from G0 to G1′ (G1′>G1) at time point T0 and then changed from G1′ to G1 at time point T1. As shown in FIG. 2B, brightness of the pixel reaches L1 at time point T1, wherein the duration between time points T0 and T1 is shorter than the duration between time points T0 and T2. Thus, by using an over-driving method, response time required for brightness change of a liquid crystal display panel from one frame to the next frame is shortened.
Taiwan Patent No. I269254 discloses an over-driving device and a method thereof. Referring to FIG. 3, an over-driving device 300 comprises a compression circuit 310, a buffer 312, two decompression circuits 314-1 and 314-2, a comparison circuit 316, a multiplexer 318, and an over-driving module 320. The compression circuit 310 receives and compresses a source signal to generate a compression data signal 311. The buffer 312 receives the compression data signal 311 to temporarily store compression data of gray values in a frame and generate a buffering data signal which is output in a next frame. The decompression circuits 314-1 and 314-2 decompress the buffing data signal 313 and the compression data signal 311 to generate decompression data signals 315-1 and 315-2, respectively. The comparison circuit 316 compares the decompression data signals 315-1 and 315-2. In other words, the comparison circuit 316 compares gray values of the pixel (not shown) in the current and previous frames and then drives the over-driving module 320 to perform following operations according to the comparison result.